(1) Field of the Invention
This invention relates to a hydraulic circuitry for a backhoe comprising a multiplex valve assembly provided with a first center bypass and including first and second control valves connected to a hydraulic cylinder for vertically oscillating an arm assembly and to a hydraulic motor for driving one of right and left traveling members, the first and second control valves being connected in parallel to each other to a first pump, and a further multiplex valve assembly provided with a second center bypass and including third to seventh control valves connected to a further hydraulic motor for driving the other traveling member, a hydraulic motor for slewing a platform, a hydraulic cylinder for flexing and stretching the arm assembly, a cylinder for actuating a bucket, and a cylinder for actuating a dozer, the third to seventh control valves being connected in parallel to one another to a second pump.
(2) Description of the Prior Art
The above circuitry for a backhoe enables the most frequently required operations to be carried out while maintaining the pumps at constant working rates, such operations including vertical oscillation of the working arm assembly by the first pump combined simultaneously with one of flexion and stretching of the arm assembly, actuation of the bucket and slewing of the platform by the second pump.
However, when a bulldozing operation is performed together with running of the vehicle, the vehicle will run obliquely. This is because the motor for driving the other traveling member and the cylinder for actuating the dozer are connected in parallel to each other to the second pump and, when the running and the bulldozing operation are effected at the same time, the flow to this motor reduces and brings its revolution rate lower than that of the other motor. To solve this problem a confluence valve may be provided in operative connection with the seventh control valve in order to connect the hydraulic cylinder for actuating the dozer to the first pump. Such a valve arrangement, however, has disadvantages of being large and costly and easy to go into disorder.
On the other hand, it is desired to improve working efficiency by using the pressure fluid of the first pump, when the first pump is at rest, to supply it confluently to the cylinder for flexing and stretching the arm assembly or to the cylinder for actuating the bucket, but not to the platform slewing motor to avoid a dangerous abrupt slewing of the platform. This requirement may be met if two confluence valves are provided to connect those motor and cylinder to a line or lines leading from the first pump and cooperate with the fifth and sixth control valves to provide confluence. Such a valve arrangement again has disadvantages of being large and costly and easy to go into disorder.